A circuit arrangement of the above-defined type is described in German Patent No. 31 53 169. Deterioration of the current transformers or the electronic tripping devices and their power supply lines cannot be detected with this circuit arrangement. If under such conditions the circuit breaker fails to trip in a timely manner in the case of a short circuit or an overload, this may cause considerable material damage in the electrical system and even serious personal injuries. Initial calibration of tripping devices has been traditionally performed in a test bay. Subsequent testing of the installed current transformers has been difficult.